(1) Field of the Invention
The present invention relates to cable fairings, and more specifically to systems and methods for automatically applying fairings to a cable as it is deployed from a winch.
(2) Description of the Prior Art
Unfaired cable has a normal drag coefficient of approximately 1.5, compared to about 0.2 for a cable with hard fairings. When an unfaired cable is deployed from a winch into a fluid medium, this increased drag significantly increases the amount of cable required to achieve a certain depth.
Despite this reality of operation, cables are often not faired because faired cables require increased winch sizes compared to non-faired cables and faired cables also increase the complexity of handling the cable. Conventional winches can typically only accommodate one layer of faired cable. Some specialized winches have been designed to accommodate two (or more) layers of faired cable by separating them with annular steel shells. However, these designs are complex and expensive.
Several fairing designs allow multiple layers of cable to be wound on a single winch. Ribbon fairing and hairy fairing are commonly used. These fairings include streamers (ribbons) or short pliant hairs attached to the cable.
Another type of fairing, known as zipper fairing, consists essentially of a sheet of reinforced polyethylene (or similar material) that is wrapped around the cable and then sealed (zipped) to itself at two free ends. These designs do reduce drag, but not nearly as much as hard fairings. Furthermore, these designs tend to be destroyed by handling systems.
Another major issue affecting automated attachment of hard fairings is the alignment of the fairing during attachment. Hard fairings are typically held together with screws. Some hard fairings have internal fasteners that snap together as the two fairing pieces are attached to the cable. Automating screw attachments onboard a ship would require a complicated attachment system. Additionally, potential misalignment problems preclude onboard automation of either of these designs.
What are therefore needed are systems and methods for automatically applying hard fairings to a cable as the cable is deployed from a winch.